[SSH & SCP] ignore known hosts

Host's key could be changed in many cases.
It's a good idea to ignore host's key if no security issues.
Add following options to ssh and scp commands to do so.

Linux / Cygwin

-o "UserKnownHostsFile=/dev/null" -o "StrictHostKeyChecking=no"

Windows

-o "UserKnownHostsFile=NUL" -o "StrictHostKeyChecking=no"

[ Cygwin64 ] - TeraTerm connection?

1. Switch to TeraTerm directory.
2. Replace the original 32-bit cygterm by 64-bit one from cygterm+-x86_64 directory.

[ Shell ] assign value

Pipeline invokes sub-shell and all changes won't be recorded, a famous bash example:

    cat file | while read line; do var_in_pipe="$line"; done

And var_in_pipe never given values, so use redirect instead.

    while read line; do var_no_pipe="$line"; done < file

[ Shell ] which is running

ps p $$ o comm=

[ Patch ] diff and patch

diff -u original modded > mod.patch

-N : absent files as empty.
-a : text mode
-r : directory recursively

patch -p N < mod.patch

-p N : strip N leading components from file names
 N=0 if diff and patch were performed under the same directory

[ Ethtool ] MAC update

As long as NIC driver supports the EEPROM can be updated via ethtool.
It's convenient on production line if the EEPROM is not well pre-burnt.

Ethtool write a byte:

ethtool -E $eth magic $mgc offset $off value $bye

mgc = magic composed by devID and venID, "lspci -n" to discover it
bye = byte to write
eth = ether device name, "ifconfig" to discover it
off = writing offset in EEPROM

A for loop can easily update the MAC address.

Example of updating Intel i210 MAC under CentOS

mgc=0x15338086
mac=00:11:22:33:44:55
eth=enP6p1s0
off=0
for i in {0..5}; do ethtool -E $eth magic $mgc offset $((off+i)) value 0x${mac:$((i*3)):2}; done

Checking the result by reading EEPROM.

ethtool -e $eth offset $off length 6

[ SSH ] remote unattended

sshpass -p <password> ssh -q -o "UserKnownHostsFile=/dev/null" -o "StrictHostKeyChecking=no" <user id>@<remote IP> "<command(s)>"

Cygwin works as well.

[ Shell ] sourced?

A quick thought is using $0 and $_ as follow, but many exceptions.

    [ "$0" != "$_" ]  && echo Sourced

A better version to tell sourced condition, but still doesn't cover all cases.

    [ "$0" = "`ps p $$ o cmd=`" ] && echo Sourced

Finally a perfect solution, cheers!

    [ "`cat /proc/$$/cmdline`" = "$0" ] && echo Sourced

However /proc/$$/cmdline may contain zero characters and grep may not support -z option, so revised again, almost universal now.

    [ "`cat /proc/$$/cmdline | xargs -0 echo`" = "$0" ] && echo Sourced!

Under bash there is a quick way to exit without quitting the console:

    return X >&/dev/null || exit X

or

    eval "return X >&/dev/null; exit X"

Where X is the exit code, assume sourced and simply returns, if failed, do exit.

Form 2 is treated as an executive unit instead of two separate commands compared to form 1 and is useful in complicated conditions which form 1 won't work, says:

    [ ... ] && command 1 && command 2 && eval "return X >&/dev/null; exit X"